• is the lowest layer of the earth’s atmosphere where temperature decreases with an
increase in height.
• consists of ¾ of the total atmosphere in weight.
• contains almost all the weather.
is the layer above the troposphere where temperature initially remains constant to an average height of 20 km then increases to reach a temperature of -2.5°C at a height of 47 km, then above 51 km temperature starts to decrease again. The reason for the increase is the action of ultraviolet radiation in the formation of ozone. The boundary
between the stratosphere and the next layer, the mesosphere is known as the stratopause. The average height of the stratopause is 50 km in temperate latitudes.
• This marks the boundary between the troposphere and the stratosphere and is where temperature ceases to fall with an increase in height. (Practically taken as the height where the temperature fall is less than 0.65°C per 100 m (2°C per 1000 ft.)
• The height of the tropopause is controlled by the temperature of the air near the surface. The warmer the air, the higher the tropopause. The colder the air, the lower the tropopause. Therefore, temperature variations due to latitude, season, land and sea, will all cause varying heights of the tropopause. There are two locations where the
tropopause abruptly changes height or “folds”. These are at approximately 40° and 60° latitude. The average height of the tropopause at the Equator is 16-18 km with an average temperature of -75°C to -80°C, and at the poles 8 km with an average temperature of -40°C to -50°C. The average value at 50°N is 11 km (36 090 ft) with a temperature of
• The temperature of the tropopause is controlled by its height. The higher it is, the colder the temperature at the tropopause. The lower it is, the warmer the temperature at the tropopause. The temperature at the tropopause can be as high as -40°C over the poles and as low as -80°C over the Equator.
The Significance of Tropopause Height
The significance of the tropopause height is that it usually marks:
• the maximum height of significant cloud.
• the presence of jet streams.
• the presence of Clear Air Turbulence (CAT). It is now referred to as TURB.
• the maximum wind speed.
• the upper limit of most of the weather